This invention relates to a new class of S-thiolcarbonate esters and to synthetic resin stabilizer compositions comprising these esters as well as to synthetic resins stabilized with such esters and with stabilizer compositions comprising these esters along with known polymer stabilizers.
The S-thiolcarbonate esters have the characteristic group ##STR4## carrying an organic group attached to sulfur and a second organic group linked to the carbonyl group through oxygen or sulfur, and can be named as carbothioic acid O,S-diesters and carbodithioic acid S,S'-diesters. The former are isomers of thiocarbonic acid O,O-diesters having the characteristic group ##STR5## and the latter are isomers of the well known xanthate esters (carbodithioic acid O,S-diesters) having the characteristic group ##STR6## The S-thiolcarbonate esters have been remarkably little studied.
The chemical literature prior to 1940, as reviewed by M. Bogemann in Houben-Weyl, "Methoden der Organischen Chemie" (4th edition, G. Thieme Verlag Stuttgart, Germany, 1955) Volume 9, pages 816-817 and 819-820, as well as by E. E. Reid in "Organic Chemistry of Bivalent Sulfur" (Chemical Publishing Co., New York 1962) volume 4, pages 135-6 and 170-71, mentions thiolcarbonate O,S-diesters having the formula RS-CO-OR' and thiolcarbonate S,S'-diesters having the formula RS-CO-SR' in which R and R' are hydrocarbon groups such as alkyl, aryl, ethylene, or benzhydryl, as well as carboxymethyl. Both reviewers cite the ready ammonolysis and hydrolysis of these thiolcarbonates by alcoholic ammonia and hot water respectively. There is no mention, however, of higher molecular weight thiolcarbonate esters substituted with carboxyalkylenethiol groups, and the synthetic methods described are in no way applicable to the preparation of such higher molecular weight thiolcarbonate esters.
More recently, W. Dial in U.S. Pat. No. 2,537,518 of Jan. 9, 1951 disclosed esters of the general structure ##STR7## in which R and R" are phenyl, tolyl, xylyl, and trimethylphenyl, R' is alkylene containing 2 to 4 carbon atoms, and n is a small whole number, prepared from a glycol bis(chloroformate) and a phenol or thiophenol. T. Kawata et al in Yakugaku Zasshi, volume 96 (1976), pages 832-840, described catalytic rearrangements of O,S-dialkyl dithiocarbonates to S,S'-dialkyl dithiocarbonates catalyzed by Lewis acids such as aluminum chloride, ferric chloride, stannic chloride, titanium tetrachloride, and boron trifluoride. All Kawata's thiolcarbonates had exclusively hydrocarbon substituents and no hint is given that Kawata's methods might be applicable to thiolcarbonates having other than hydrocarbon substituent groups. J. Krenzer in U.S. Pat. No. 4,040,812 of Aug. 9, 1977 disclosed compounds of the formula ##STR8## wherein R.sup.1 is selected from the group consisting of lower alkyl, lower alkenyl, lower chloroalkyl, lower bromoalkyl, trifluoromethyl, lower alkoxy, lower alkylthio, lower alkylsulfonyl, lower alkylsulfinyl and cycloalkyl of from 3 to 7 carbon atoms; R.sup.2 is selected from the group consisting of lower alkyl, lower alkenyl, lower chloroalkyl, lower bromoalkyl and ##STR9## wherein R.sup.3 and R.sup.4 are each selected from the group consisting of hydrogen and lower alkyl; Z is selected from the group consisting of oxygen and sulfur; and R.sup.5 is selected from the group consisting of lower alkyl, lower chloroalkyl, lower bromoalkyl, lower alkenyl, lower alkynyl, lower alkoxyalkyl, cycloalkyl of from 3 to 7 carbon atoms and ##STR10## wherein X is selected from the group consisting of lower alkyl, halogen, lower haloalkyl, nitro, cyano and lower alkoxy, and m and n are each integers from 0 to 3.
T. Y. Shen et al in U.S. Pat. No. 4,057,637 of Nov. 8, 1977 disclosed compounds of structural formula ##STR11## or pharmaceutically acceptable salt thereof, wherein m is 0 or 1;
R is C.sub.1-5 alkyl; PA1 R.sub.31 groups are the same or different and are hydrogen ##STR12## where R.sub.40 is C.sub.1-5 alkyl or C.sub.2-5 alkenyl, R.sub.32 is hydrogen or ##STR13## with the proviso that if both R.sub.31 groups are hydrogen or m is 0, then R.sub.32 is not hydrogen. PA1 R.sub.a is --CH.sub.2 (CH.sub.2).sub.n COOR' or alkyl PA1 n=1 to 5 PA1 m=1 to 16 PA1 R is an alkyl of 8 to 30 carbon atoms, PA1 m and n are each integers of 2 or 3, PA1 R' is an alkylene containing 2 to 12 carbon atoms, PA1 R" is an alkyl containing 1 to 20 carbon atoms, PA1 X is hydrogen or --OC--C.sub.n H.sub.2n SR, at least one of which is --OCC.sub.n H.sub.2n SR, PA1 the R.sub.1,R' and R" moieties in one compound being the same or different. PA1 In which y has a value of from 2 to 18 when n is 2 and a value of from 3 to 6 when n is greater than 2, the value of y is all cases being equal to or greater than that of n.
None of these disclosures includes a thiolcarbonate ester having carboxyalkylene groups linked to sulfur, and there has been no disclosure of any thiolcarbonate ester included in a synthetic resin stabilizer.
Sulfur compounds used in synthetic resin stabilizers have been mostly mercaptans, metal and organometallic mercaptans, disulfides, and thioethers such as dialkyl sulfides and thioalkylenecarboxylic acid esters.
The pioneer disclosure of thioether carboxylic acid esters for stabilizing a polymer is believed to be M. Gribbins in U.S. Pat. No. 2,519,755 of Aug. 22, 1950 of Aug. 22, 1950. Griggins stabilized ethylene polymers with 0.001% to 5% by weight of a beta-thioether of an ester of propionic acid having the formula: EQU ROOCCH.sub.2 CH.sub.2 S--X,
in which R is an alkyl or a cycloalkyl radical such as n- and isobutyl, amyl, heptyl, nonyl, decyl, lauryl, glycyl, cinnamyl, capryl, benzyl, allyl, cetyl, stearyl, palmityl, cyclohexyl, and similar groups, and X is:
1. a hydrocarbon group such as, e.g., the alkyl groups: methyl, ethyl, propyyl, butyl, lauryl; the aryl groups; phenyl, naphthyl, benzyl; and such groups as p-methoxy phenyl, p-hydroxyphenyl and cyclohexyl.
2. an oxygenated-hydrocarbon group such as, e.g., the alcohol groups; hydroxymethylene, hydroxyethylene, and hydroxybutylene; the ether groups; methoxymethylene, methoxyethylene and ethoxyethylene; and acid groups and the R esters thereof;
carboxymethylene, carboxyethylene, carboxypropylene and carboxybutylene; and aldehyde radicals as aldehydoethyl.
3. a sulfur-hydrocarbon group such as, e.g., mercaptoethyl, mercaptopropyl, mercaptobutyl, mercaptoisobutyl, mercaptohexyl and ethiaethyl.
4. a sulfur-and oxygenated-hydrocarbon group such as, e.g., carboxyethiaethyl (CH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 COOH).sub.2 carboxyethiaethyldithiaethyl (CH.sub.2 CH.sub.2 SSCH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 COOH), carboxyethiaisobutyl (CH.sub.2 CH.sub.2 CH(CH.sub.3)SCH.sub.2 CH.sub.2 COOH) and carboxyethiapropyl (CH.sub.2 CH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 COOH).
5. a sulfur-and nitrogen-containing hydrocarbon group such as, e.g., 3-benzothiazyl mercaptopropionic acid, specifically described in U.S. Pat. No. 2,397,960.
Among these, Gribbins found the di-higher alkyl beta-thiodipropionates and especially the dilauryl and distearyl esters outstanding. Subsequently, thioether carboxylic acid esters and in particular thiodipropionates have been employed in conjunction with other stabilizers such as a polyhydric phenol in the stabilization of polypropylene and other polyolefins against degradation upon heating or ageing under atmospheric conditions. Disclosures by C. Tholstrup, U.S. Pat. Nos. 3,033,814 of May 8, 1962 and U.S. Pat. No. 3,160,680 of Dec. 8, 1964; L. Rayner, U.S. Pat. No. 3,181,971 of May 4, 1965; D. Bown, U.S. Pat. No. 3,242,135 of Mar. 22, 1966; S. Murdock, U.S. Pat. No. 3,245,949 of Apr. 12, 1966; H. Hagemeyer, U.S. Pat. No. 3,282,890 of Nov. 1, 1966; J. Casey, U.S. Pat. No. 3,496,128 of Feb. 17, 1970 and U.S. Pat. No. 3,586,657 of June 22, 1971; M. Minagawa, U.S. Pat. No. 3,549,572 of Dec. 22, 1970, U.S. Pat. No. 3,629,189 of Dec. 21, 1971, U.S. Pat. No. 3,673,152 of June 27, 1972, U.S. Pat. No. 3,849,370 of Nov. 19, 1974 and U.S. Pat. No. 3,869,423 of Mar. 4, 1975; W. Drake U.S. Pat. No. 3,624,026 of Nov. 30, 1971; A. DiBattista, U.S. Pat. No. 3,824,192 of July 16, 1974; B. Cook, U.S. Pat. No. 3,850,877 and H. Mueller U.S. Pat. No. 3,850,918 of Nov. 26, 1974; M. Dexter U.S. Pat. No. 3,856,748 of Dec. 24, 1974; U.S. Pat. No. 3,888,824 of June 10, 1975, and U.S. Pat. No. 3,903,160 of Sept. 2, 1975; P. Klemchuk U.S. Pat. No. 3,860,558 of Jan. 14, 1975; M. Rasberger U.S. Pat. No. 3,867,340 of Feb. 18, U.S. Pat. No. 3,901,931 of Aug. 26, 1975; H. Brunetti U.S. Pat. 3,867,337 of Feb. 18 and U.S. Pat. No. 3,873,498 of Mar. 25, 1975; S. Rosenberger U.S. Pat. No. 3,884,874 of May 20 and U.S. Pat. No. 3,887,518 of June 3, 1975; C. Ramey U.S. Pat. No. 3,907,803 of Sept. 23, 1975 are representative of a very large number of stabilizer combinations including dilauryl and distearyl thiodipropionate or other dialkyl thiodipropionates along with polyhydricphenols and sometimes organic phosphites, metallic stearates, ultraviolet absorbers, nickel compounds, and heavy metal deactivators for use in polypropylene and other polyolefins.
Thiodipropionate esters are also used in stabilizer combinations for other polymers such as elastomeric glycol-terephthalic acid polyesters disclosed by A. Bell in U.S. Pat. No. 3,157,619 of Nov. 17, 1964; high molecular weight polymers of formaldehyde disclosed by R. Green in U.S. Pat. No. 3,228,885 of Nov. 29, 1966, organotin compound stabilized polyvinyl chloride disclosed by O. Kauder in U.S. Pat. No. 3,297,629 of Jan. 10, 1967 and C. Stapfer in U.S. Pat. 3,890,276 of June 17, 1975; acrylonitrile-butadiene-styrene (ABS) polymers disclosed by W. Cummings U.S. Pat. No. 3,267,069 of Aug. 16, 1966; A. Hecker U.S. Pat. No. 3,472,813 of Oct. 14, 1969 and P. Marinacci U.S. Pat. No. 3,637,555; and polyamides disclosed by T. White in U.S. Pat. No. 3,904,705 of Sept. 9, 1975. The polyhydric phenol is believed to function as an antioxidant in such combinations, and the thiodipropionate ester is often termed a costabilizer, Secondary stabilizer, synergist, or decomposer of organic peroxides.
While dialkylthiodipropionates have many favorable attributes such as availability in high purity at reasonable cost, a low degree of toxicity, and generally good stabilizing effectiveness, certain problems attendant on their use have long been recognized, particularly the need to use high concentrations in certain highly stressed formulations to obtain the required heat stability, and a tendency to lose effectiveness in use as a result of exposure to the leaching action of moving streams of warm water and warm air as in the washing and drying cycles of automatic dishwashers and laundry machines.
Attempts to improve on these characteristics have included the use of more efficient and more permanent thiodipropionate esters as well as more effective antioxidants and stabilizer combinations. Thus A. Hecker in U.S. Pat. No. 3,244,650 of Apr. 5, 1966 disclosed a stabilizer system for polypropylene composed of three stabilizers: an organic polyhydric phenol, an organic phosphite and a polyvalent metal salt of an organic acid. To this system, U.S. Pat. No. 3,255,136 of June 7, 1966 added a fourth ingredient, a thiodipropionic acid ester having the formula: EQU R.sub.1 OOCCH.sub.2 CH.sub.2 --S--CH.sub.2 CH.sub.2 COOY
in which R.sub.1 is an organic radical selected from the group consisting of hydrocarbon radicals such as alkyl, alkenyl, aryl, cycloalkyl and mixed alkyl aryl and mixed alkyl cycloalkyl radicals; hydroxyalkyl and hydroxyalkyloxyalkylene radicals; and esters thereof with aliphatic carboxylic acids; and Y is selected from the group consisting of (a) hydrogen, (b) a second R radical R.sub.2, which can be the same as or different from the R.sub.1 radical, (c) a polymeric chain of n thiodipropionic acid ester units: EQU --XO(OCCH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 COOXO).sub.n OCCH.sub.2 CH.sub.2 --S--CH.sub.2 CH.sub.2 COOZ
where Z is hydrogen, R.sub.2 or M, n is the number of thiodipropionic acid ester units in the chain, and X is a bivalent hydrocarbon group of the type of R.sub.1, that is, alkylene, alkenylene, cycloalkylene, mixed alkylene-arylene and mixed alkylene-cycloalkylene radicals: hydroxyalkylene and hydroxyalkyloxyalkylene radicals; and esters thereof with aliphatic carboxylic acids; and
(d) a polyvalent metal M of Group II of the periodic table such as zinc, calcium, cadmium, barium, magnesium and strontium.
The molecular weights of the R and Y radicals are taken such that with the remainder of the molecule the thiodipropionic ester has a total of from about ten to about sixty atoms per sulfur atom.
U.S. Pat. No. 3,378,516, patented Apr. 16, 1968 to Tholstrup, Bell and Kibler, proposes combinations including linear thiodi alkanoate polyesters obtained from a thiodialkanoic acid and a diol having a molecular weight of from about 500 to 4000, together with a phenolic antioxidant and/or a phosphite. These combinations are said to display synergistic stabilizing effectiveness.
H. Schirmer in U.S. Pat. No. 3,598,776 of Aug. 10, 1971, disclosed that the incorporation of 10% by weight disproportionated resin in polypropylene enabled him to use 2% by weight dilaurylthiodipropionate (LTP) in the polymer without blooming while in the absence of the rosin only 1% could be used without blooming and the stability of the polymer with the rosin that the higher LTP concentration was significantly increased.
H. Schutze in U.S. Pat. No. 3,630,991 of Dec. 28, 1971 disclosed non-exuding and non-volatile sulfur containing esters of cyclic terpene alcohols for the stabilization of 2 to 8 carbon alpha-olefin polymers together with hindered phenols. Schutze's esters may be represented by the structural formulae EQU ROOC CH.sub.2 (CH).sub.n SR.sub.a EQU ROOC CH.sub.2 (CH.sub.2).sub.n SS(CH.sub.2).sub.n CH.sub.2 COOR' ##STR14## EQU ROOC CH.sub.2 (CH.sub.2).sub.n S(CH.sub.2).sub.n S(CH.sub.2).sub.n CH.sub.2 COOR' EQU ROOC CH.sub.2 (CH.sub.2).sub.n S(CH.sub.2).sub.n S(CH.sub.2).sub.m CH.sub.3
where
R is a radical selected from the group consisting of abietyl, hydroabietyl, tetrahydroabietyl, dihydroabietyl, dehydroabietyl, dihydropimaryl, tetrahydropimaryl, borneyl, alpha-terpineyl, B-terpineyl, V-terpineyl, methyl, and dihydroterpineyl, and
R' is a radical selected from the group consisting of abietyl, hydroabietyl, tetrahydroabietyl, dihydroabietyl, dehydroabietyl, dihydropimaryl, tetrahydropimaryl, borneyl, alpha-terpineyl, B-terpineyl, methyl, and dihydroterpineyl.
A. Onishi, in U.S. Pat. No. 3,629,194 of Dec. 21, 1971 disclosed a polyolefin resin stabilized against thermal aging with esters of alkyl thiopropionic or alkyl thiobutyric acid with a polyol having up to five hydroxyl groups, in combination (optionally) with a phenolic antioxidant. The alkyl thiopropionic or alkyl thiobutyric acid esters are defined as having one of the formulae: EQU R-SC.sub.n H.sub.2n COOR'OOCC.sub.n H.sub.2n SR (1) EQU RSC.sub.n H.sub.2n COOC.sub.m H.sub.2m SC.sub.m H.sub.2m OOCC.sub.n H.sub.2n SR (2) EQU R"C(CH.sub.2 OX).sub.3 ( 3) ##STR15## and EQU C--CH.sub.2 OX).sub.4 ( 5)
wherein
The phenolic antioxidants are defined by Onishi as mono-or polyhydric phenolic compounds in which at least one of the ortho positions to a hydroxyl group is substituted by an alkyl, aralkyl, or cycloalkyl group.
The substituents preferably contain carbon atoms of a number of the order of 3 to 10, and the alkyl group, inclusive of that in an aralkyl and cycloalkyl groups can be unsaturated. The phenolic compounds may be further substituted, and the phenolic compounds may be polyphenolic compounds such as bisphenolic, trisphenolic, or tetrakisphenolic compounds in which phenolic nuclei are connected by a connecting group such as an alkylene, a thioether, or a triazinoxyl group.
M. Dexter in U.S. Pat. No. 3,758,549 of Sept. 11, 1973 disclosed alkyl esters derived from alkyl thioalkanoic acids and alkane polyols, such as pentaerythritol tetrakis, 3-n-dodecylthiopropionate, and ethylene-bis-3-n-dodecylthiopropionate. These are used in combination with phenolic antioxidants to effectively stabilize polyolefins from the deleterious effects of heat and oxygen. The alkyl esters are defined by the formula: ##STR16## wherein R is an alkyl group of from one to eighteen carbon atoms, n has a value of from 2 to 4; and Z is an aliphatic hydrocarbon of the formula: EQU C.sub.y H.sub.2y+2-n
M. Minagawa in Japanese Kokai 75/106881 of Aug. 27, 1975 disclosed stabilized resin compositions containing 3-alkylthiopropionate esters of alcohols containing a nitrogen-heterocyclic ring, for example tris(2-hydroxyethyl isocyanurate) and optionally a phenolic antioxidant.
E. Schurdak in U.S. Pat. No. 3,966,675 of June 29, 1976 has disclosed mixtures of pentaerythritol tetrakis(3-n-dodecylthiopropionate) with bis(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) dithiolterephthalate or 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-s-triazine-2,4,6-trione that are stated to be extremely effective in inhibiting the thermal degradation of polypropylene.
There have also been disclosures of improved stabilization of olefin polymers, vinyl chloride polymers, and other synthetic resins with thiodipropionate esters used together with special phenolic condensation products. Thus D. Bown et al. in U.S. Pat. No. 3,510,507 of May 5, 1970 and U.S. Pat. No. 3,691,132 of Sept. 12, 1972 disclosed polyolefins stabilized with polyphosphites, polyphosphates, polyphosphonites, polyphosphonates, polyborates, polycarbonates, and polysilanes which are condensation products of a 4,4'-bisphenol with a condensing or linking agent which may be of the ester type, such as the esters of triaryl or mixed aryl-alkyl compounds, or the acid halide type. Bown's condensation product stabilizers have molecular weights between 600 and 8000 or higher and are described by the structural formula, ##STR17## where X is selected from the group consisting of ##STR18## --C--C, and C--A--C-- where A is a C.sub.1 to C.sub.16 alkylene or an arylene; R', R", R''', and R'''' are selected from the group consisting of hydrogen, C.sub.1 to C.sub.18 alkyls, and an aryl group; Y is selected from the group of ##STR19## where R is hydrogen, a C.sub.1 to C.sub.18 alkyl, or aryl; ##STR20## where m is 0 to 10, preferably 4 to 8, ##STR21## where A' is (CH.sub.2).sub.n --S--(CH.sub.2).sub.n or --(CH.sub.2).sub.n --S--(CH.sub.2).sub.m --S--(CH.sub.2).sub.n where n is 0 to 10, preferably 2 and m is 0 to 10, preferably 5; ##STR22## where R is an alkyl, preferably methyl, and Z is ##STR23## where R', R", R''', R'''', and X correspond respectively to the R',R",R''',R'''', and X previously selected when n has a value from 1 to 15, or Z may be derived from the compound used to introduce Y into the product when n has a value from 2 to 15, for example --R or --OR where R is hydrogen, an alkyl, or aryl. When Y in the formula of Bown's stabilizer is ##STR24## the stabilizer is a type of hydroxyaryl phosphite. Similarly, when Y in the formula is ##STR25## the stabilizer is a hydroxyaryl carbonate.
Bown's condensation products are described as especially effective in high molecular weight solid polyolefins when used together with a dialkyl sulfide costabilizer such as dilauryl thiodipropionate, distearyl thiodipropionate, ditridecyl thiodipropionate, dicetyl sulfide, bis(tetradecylmercapto) paraxylylene, and 10,24-dithiotetracontane.
J. Floyd et al U.S. Pat. No. 4,032,510 of June 28, 1977, disclosed low molecular weight polycarbonate esters of bisphenols such as 2,2-bis(3-t-butyl-4-hydroxyphenylpropane) and 4,4'-butylidene bis(6-t-butyl-3-methylphenol) prepared in such a way as to contain few or no free phenolic hydroxyl groups as being highly effective heat and light stabilizers for polyolefins and giving a synergistic effect with distearyl thiodipropionate, tris (nonylphenyl) phosphite, and distearyl pentaerythritoldiphosphite.